is 190K Miles on a 2001 cummins with a 5.9 24V too many miles?

Find out what maintenance was done. The front ends and wheel bearings are high maintenance for these. Injectors can be very dear to replace too. Ask if any have been replaced and when.

Other then that good truck and motor.

Cheers Don.

P.S. have a buddy with hydrogen injector on it and lots of power and good on fuel.

If it's been maintained well, then not really.

Ball joints, trac-bars, and wheel bearings are all the weak link in the front end. The 24V engines don't have the injector problems that the newer trucks do, but they are extremely prone to failing lift pumps which will take out the injection pump. That's about a $1500 hit right there by the time you buy a lift pump, injection pump, and a gauge or light to monitor your fuel pressure and help prevent future problems.

Automatics are weak, but can be built into a very stout unit. At stock power levels the 6-speeds are fairly bulletproof. Run a good synthetic fluid and over fill them by a couple quarts more than the recommended capacity and they'll last forever. 5-speeds are decent, but prone to 5th gear nut backing out. Relatively simple fix though.